This invention relates to apparatus for treating solid, granular and aggregate materials and in particular to an apparatus for accomplishing the preheating, post reclamation and cooling of spent, i.e., used, chemically bonded foundry sand.
Although most people do not commonly view sand as being one of our Nation's diminishing natural resources, to those in the foundry field the shrinking supply of sand of the kind that is suitable for use for foundry purposes is a matter of concern. More specifically, despite the fact that some kinds of sand may be considered to be in relatively plentiful supply, the specific type of sand which is capable of being employed for purposes of making castings through the use of processes associated with foundry operations is, generally speaking, in relatively short supply. That is, the latter type of sand, which for ease of reference will hereinafter be referred to generically by the term "foundry sand" occurs naturally in only selected locations. Accordingly, as the foundry sand continues to be removed from any given one of these selected locations, the supply of foundry sand thereat eventually becomes exhausted. This is precisely what is taking place more and more frequently these days. As a consequence, those employed in the foundry industry who are responsible for acquiring supplies of foundry sand are reaching the point where they can no longer satisfy their requirements for foundry sand simply from local sources. Rather, they are being forced to seek supplies of foundry sand from sources located at ever increasing distances from the site of the foundry at which it is intended to make use of the foundry sand.
Apart from that concern to which reference has been had hereinbefore, which those in the foundry field have with regard to the fact that available sources of supply of foundry sand are becoming fewer and fewer in number, there is yet another matter, which is of concern to those in the foundry industry. This is the matter of the increasing rise in the price of the foundry sand which is available. This increase in the cost of obtaining adequate supplies of foundry sand appears to be occasioned basically by three factors.
The first of these is the fact that sources of supply of available foundry sand are located further and further away from the individual foundry sites. Thus, that segment of the price of foundry sand which is represented by the cost of transporting the foundry sand to the foundry site is becoming a more and more significant factor in the overall cost of obtaining the foundry sand.
The second is a function of the fact that foundry sand is in dwindling supply. Namely, one finds that in the case of most items, as the item becomes less and less available, the price of the item increases in inverse relation to the extent to which the item is available. So it is in the case of foundry sand. Further, as a corollary to this, and something which is particularly true in the case of natural resources, the first of the known natural resources to be removed commonly is that which is the easiest to remove. Thereafter, only after that which is easiest to remove is removed is removal had of that which is more difficult to remove. Concomitantly, the price of the natural resource, e.g., foundry sand, increases in proportion to the cost of removing the natural resource, which in turn normally is a function of the degree of difficulty encountered in effecting the removal of the natural resource.
The third, which is of equal if not in some instances greater concern, that is faced by those in the foundry field is that presented by the fact that it is becoming increasingly more common to find that chemically bonded sand is no longer being accepted for disposal at local disposal sites. That is, from an ecological standpoint, environmental protection agencies on the local level are prohibiting the disposal of such chemically bonded sand at disposal sites which fall within their respective jurisdictions. Thus, those in the foundry field are in need of finding a way of accomplishing the disposal of such chemically bonded sand in a safe and legally accepted fashion.
As can be seen by reference to the prior art, there have been attempts made previously in an effort to address one or more of the above-noted concerns. In this regard, the focus of one of these prior art attempts has been on an effort to effect the reclamation of foundry sand. One rationale behind this effort has been that if it were to prove possible to effect a recycling of the foundry sand, this would go far towards forestalling the exhaustion of existing sources of supply of foundry sand. Furthermore, to the extent that recycling of the foundry sand takes place at or in relatively close proximity to the individual foundry sites whereat the use was originally made of the foundry sand, the effect thereof would be to negate substantially if not totally, the need to incur the expenses associated with the transportation of foundry sand from the sources of supply thereof to the foundry sites. In addition, the ability to reclaim used foundry sand obviates the problem associated with the need to find a suitable disposal site for the used foundry sand.
Insofar as the reclamation of used foundry sand is concerned, there are at least two major requirements, which from a practical standpoint, must be satisfied thereby. Namely, the used foundry sand after being subjected to the reclamation process must be in substantially the same condition as it originally was. That is, the reclamation process must be capable of restoring the used foundry sand to, in essence, its original condition. Secondly, the reclamation of used foundry sand must be capable of being accomplished economically. More specifically, the cost of reclamation must be such that reclamation from a financial standpoint is sufficiently attractive to render it desirable to undertake the investment in terms of time, labor and money required thereby as compared to continuing to purchase new, i.e., not previously used, foundry sand.
With respect to the matter of the reclamation of used foundry sand, a variety of different types of apparatus have been proposed for use. These apparatus may, for ease of reference, be classified into categories according to the type of treatment to which the used foundry sand is subjected for purposes of effecting the reclamation thereof. Thus, one category into which such apparatus may be placed is that of mechanical units. Here, reliance is had, generally speaking, on some form of abrasive action in order to effect the removal of, for example, organic coatings from the particles of sand. This abrasive action may be realized through the action of some sort of mechanical member, or through the use of a so-called "air scrubber". The latter refers to a type of device wherein the sand particles are accelerated to relatively high velocities by means of compressed air such that a rubbing action is caused to occur between individual particles of sand. In other instances, the sand particles after being accelerated are made to impinge against a suitably selected surface such that as a result of this impingement the coating fractures and separates from the individual sand particles. For purposes of illustration of a mechanical unit which has been proposed in the prior art for use in connection with the reclamation of foundry sand, reference may be had to U.S. Pat. No. 4,283,015, that issued on Aug. 11, 1981. This patent depicts on apparatus which is intended to be employed for purposes of removing no-bake coatings from foundry sand. At this point, it is deemed important that notice be taken of the fact that one should not gain the impression that in order for one to provide a system for effecting the reclamation of used foundry sand, one need only be concerned with the matter of removing organic coatings from sand particles. For, depending on the condition of the foundry sand that it is desired to reclaim, which in turn is a function of the manner in which the foundry sand has been used, a number of other considerations may be of equal, if not greater importance. For example, significant amounts of used foundry sand are produced during foundry operations wherein the used foundry sand is replete with organic matter, metal, dust and fines.
Attempts have been made, though, to provide systems of a mechanical type which would be commercially acceptable for use to effect the removal of organic matter, dust and fines from used foundry sand. However, the mechanical systems which have been made use of commercially to date have not, particularly in terms of their operation, proven to be entirely satisfactory from a performance standpoint. For example, an undesirable feature of such commercially available prior art forms of mechanical foundry sand reclamation systems is that they frequently suffer from an inability to effect the removal to the extent desired, of the organic matter from the foundry sand that is being reclaimed. The result, thus, is that subsequently conducted foundry operations are less cost effective, when used foundry sand that has been inadequately reclaimed is employed therein, because an additional amount of new sand must be mixed therewith.
A second category of apparatus that has been proposed for use in the prior art to effect the reclamation of used foundry sand is that of thermal units. In accord therewith, heat is employed for purposes of accomplishing the removal of organic coatings from the sand particles. By way of exemplification in this regard, there has previously been issued on Aug. 22, 1972 to the Applicant of the present invention, U.S. Pat. No. 3,685,165. The latter patent is directed in particular to an apparatus for thermally reclaiming resin coated sand.
Continuing to focus on the matter of the thermal reclamation of used foundry sand, and in particular that kind of foundry sand which has organic matter, metal, dust and fines present therein, there are a number of factors to which it is desirable that consideration be given if a thermal foundry sand reclamation system is to be provided that will prove to be viable from a commercial standpoint. More specifically, such a thermal foundry sand reclamation system must be capable of accomplishing the removal of the organic matter from the used foundry sand while at the same time leaving the metal that is also present in the used foundry sand in such a form as to enable it subsequently to be readily removed. Thus, one of the factors that must be taken into account in this regard is that of being able to provide sufficient heat to the used foundry sand so that the organic matter present therein is burned away. However, the operating characteristics of the thermal system must be such that the used foundry sand is not heated excessively, i.e., to such a high temperature that the heat produced is sufficient to effect a change in the state of the metal which is present in the used foundry sand. To this end, such a thermal system for reclaiming used foundry sand must possess the capability of enabling the organic matter to be burned away, while at the same time that this is being accomplished ensuring that the metal, be it of a ferrous or nonferrous nature, which the used foundry sand contains, is not adversely affected, i.e., rendered more difficult to remove, as a consequence of being exposed to the heat that is employed to burn away the organic matter. In this regard, note is taken here of the fact that some nonferrous metals, e.g., aluminum and zinc, have a significantly different melting temperature than do ferrous metals, and consequently must be treated differently from a temperature standpoint.
Another factor which must be borne in mind when one attempts to provide such a thermal system for reclaiming used foundry sand which contains organic matter, metal, dust and fines is that of the nature of the treatment which should be accorded to the fumes that are generated as the organic matter is being burned away. There are two aspects to this. The first is that of ensuring that such fumes do not pose a danger to the personnel who are attending to the operation of the thermal foundry sand reclamation system. The second is that of ensuring that any fumes which may be exhausted to the atmosphere do not constitute a source of pollutants. That is, that the fumes which are exhausted to the atmosphere as a consequence of the operation of such a thermal system for reclaiming used foundry sand do not violate the regulations applicable thereto as established by the local, state and federal authorities having cognizance over such matters.
The third factor to which it is essential that consideration be given in providing such a thermal foundry sand reclamation system is the matter of the cost thereof. Namely, both in terms of originally providing the system and in terms of operating the system thereafter, the expenditures required therefor must be such as to render it desirable to undertake the requisite investment as compared to the expenditure of the funds necessary to acquire new foundry sand rather than reclaimed foundry sand.
Related to this matter of cost, which is addressed in the preceding paragraph, is the matter of the production output of reclaimed foundry sand that can be realized through the use of such a thermal foundry sand reclamation system. Reference is had here to the fact that for such a thermal foundry sand reclamation system to be commercially viable, it is necessary that the system embody the capability of providing reclaimed foundry sand in the desired quantities, i.e., in amounts sufficient to meet the need therefor as it exists at any given site at which foundry operations capable of making use thereof take place.
In summary, the salient point which the preceding discussion serves to make is the fact that there already has been shown to exist in the prior art a need for a system which is operative to effect the reclamation of used foundry sand. And in particular the preceding discussion evidences the need in the prior art for a system that is operative to reclaim used foundry sand which contains metal of either a ferrous or nonferrous nature, organic matter, dust and fines. To meet this need a thermal sand reclamation system has been proposed. The latter system as well as the individual components which are embodied in this system comprise the subject matter of the five earlier filed patent applications to which reference has previously been made hereinbefore; namely, U.S. patent application Ser. No. 369,069, now U.S. Pat. No. 4,487,372; U.S. patent application Ser. No. 369,068; U.S. patent application Ser. No. 369,334, now U.S. Pat. No. 4,429,642; U.S. patent application Ser. No. 369,476, now abandoned; and U.S. patent application Ser. No. 369,335, now abandoned.
In accord with the mode of operation of the thermal sand reclamation system that comprises the subject matter of the above-enumerated U.S. Patent Applications the used foundry sand in order to accomplish the thermal reclamation thereof is required to be heated to a temperature approximating 1300.degree. F. To this end, when the used foundry sand contains metal of a ferrous nature, it can be heated to a temperature approximating 1300.degree. F., but when the used foundry sand contains metal of a nonferrous nature, it can not be heated to a temperature that exceeds approximately 900.degree. F. until the nonferrous metal has been separated therefrom whereupon the used foundry sand can be heated to a temperature approximating 1300.degree. F. Such temperatures are required in order to effect the thermal removal of organic matter from the used foundry sand. Thereafter, the used foundry sand from which the organic matter has been removed is required to be cooled to a temperature at which it no longer poses a hazard to humans. To heat the used foundry sand to the elevated temperatures noted above requires considerable energy to be expended. Conversely, when the used foundry sand is being cooled after being thermally reclaimed, the sand gives off considerable heat.
As a consequence of providing the aforereferenced system for reclaiming used foundry sand there has, therefore, also been shown to exist a need in the prior art for a new and improved form of apparatus that would be suitable for employment for purposes of effecting the preheating of the used foundry sand in preparation to the latter being subjected to the thermal removal of organic matter therefrom. That is, a need has now been evidenced for an apparatus that could be cooperatively associated with a thermal reclaimer apparatus in a thermal sand reclamation system, and which would be operative to accomplish the preheating of the used foundry sand prior to the latter being subjected to thermal reclamation, and wherein the preheating of the used foundry sand would take place as a consequence of a heat exchange between used foundry sand that is in the process of being cooled following the thermal removal of organic matter therefrom and used foundry sand which is about to have the organic matter thermally removed therefrom. It is, therefore, an object of the present invention to provide a new and improved form of apparatus for treating solid, granular and aggregate materials.
It is another object of the present invention to provide such an apparatus which is particularly suited for use in a thermal sand reclamation system for purposes of effecting the preheating of used foundry sand.
It is still another object of the present invention to provide such a preheating apparatus which can also be employed in a thermal sand reclamation system for purposes of effecting the post reclamation of used foundry sand.
A further object of the present invention is to provide such a preheating and post reclamation apparatus which can also be employed in a thermal sand reclamation system for purposes of effecting cooling of the used foundry sand.
A still further object of the present invention is to provide such a preheating, post reclamation and cooling apparatus which can be cooperatively associated in operative relation with a thermal reclaimer apparatus in a thermal sand reclamation system.
Yet a further object of the present invention is to provide such a preheating, post reclamation and cooling apparatus wherein also the amount of organic in the foundry sand is reduced by prereclamation, i.e., partial reclamation, of the foundry sand that is to be subjected to thermal reclamation.
Yet another object of the present invention is to provide such a preheating, prereclamation, post reclamation and cooling apparatus wherein any foundry sand lumps that may be left are crushed without the crushing of other friable materials such as ceramics inasmuch as the sand lumps do not have any tensile strength because of having been subjected to prereclamation.
Yet a still further object of the present invention is to provide such a preheating, prereclamation, crushing, post reclamation and cooling apparatus wherein the preheating of used foundry sand is accomplished as a consequence of a heat exchange between used foundry sand that has been subjected to thermal reclamation and used foundry sand that is to be subjected to thermal reclamation.
Yet still another object of the present invention is to provide such a preheating, prereclamation, crushing, post reclamation and cooling apparatus wherein removal of metal from the used foundry sand is accomplished therewithin before the used foundry sand is made to enter the thermal reclaimer apparatus.
Yet still an additional object of the present invention is to provide such a preheating, prereclamation, crushing, metal separation, post reclamation and cooling apparatus which is characterized in that it is easy to employ, it is reliable in operation, yet is relatively inexpensive to provide.